Boron phosphide-based semiconductor light-emitting device and production method thereof

ABSTRACT

A boron phosphide-based semiconductor light-emitting device, comprising: a crystalline substrate; a first semiconductor layer formed on said crystalline substrate, said first semiconductor layer including a light-emitting layer, serving as a base layer and having a first region and a second region different from the first region; a boron phosphide-based semiconductor amorphous layer formed on said first region of said first semiconductor layer, said boron phosphide-based semiconductor amorphous layer including a high-resistance boron phosphide-based semiconductor amorphous layer or a first boron phosphide-based semiconductor amorphous layer having a conduction type opposite to that of said first semiconductor layer; a pad electrode formed on said high-resistance or opposite conductivity-type boron phosphide-based semiconductor amorphous layer for establishing wire bonding; and a conductive boron phosphide-based crystalline layer formed on said second region of said first semiconductor layer, said conductive boron phosphide-based crystalline layer extending optionally to a portion of said boron phosphide-based semiconductor amorphous layer, wherein said pad electrode is in contact with said boron phosphide-based semiconductor crystalline layer at a portion of said pad electrode above the bottom of said pad electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional of application Ser. No. 10/540,995 filed Jun. 28,2005, which is a 371 of PCT Application No. PCT/JP03/16816 filed Dec.25, 2003, which claims benefit under 35 U.S.C. §111(a) claiming benefitpursuant to 35 U.S.C. §119(e)(1) of the filing date of the ProvisionalApplication No. 60/438,997 filed on Jan. 10, 2003, pursuant to 35 U.S.C.§111(b), the above-noted applications incorporated herein by referencein their entirety.

FIELD OF THE INVENTION

The present invention relates to a boron phosphide-based semiconductorlight-emitting device which attains high emission intensity and which isequipped with a pad electrode having a structure for effectivelyproviding a wide emission area, and to a method for producing the same.

BACKGROUND ART

In recent years, there have been disclosed techniques for fabricating alight-emitting device such as a light-emitting diode (abbreviated asLED) and a laser diode (abbreviated as LD) from a layer formed of boronphosphide (chemical formula: BP), which is a type of Group III-Vcompound semiconductor (see, for example, U.S. Pat. No. 6,069,021). Aboron phosphide-based semiconductor tends to form a p-type conductivelayer, because the effective mass of a hole is smaller than that of anelectron (see, for example, Japanese Patent Application Laid-Open(kokai) No. 2-288388). Recently, a light-emitting device is known tohave a p-type boron phosphide layer serving as an electrode-forminglayer (contact layer) for forming an Ohmic electrode (see, for example,Japanese Patent Application Laid-Open (kokai) No. 10-242567).

Specifically, a conventional p-type electrode formed so as to attaincontact with the p-type boron phosphide contact layer which is providedon a light-emitting layer made of a Group III nitride semiconductor isfabricated from a single layer made of a gold (symbol of element:Au)-zinc (symbol of element: Zn) alloy (see the above Japanese PatentApplication Laid-Open (kokai) No. 2-288388). Generally, in aconventional boron phosphide-based semiconductor light-emitting devicehaving an electrode also serving as a pad electrode for establishingwire bonding and being provided on a boron phosphide layer, the padelectrode is formed so as to attain contact with a surface of a p-typeor n-type boron phosphide layer (see, for example, Japanese PatentApplication Laid-Open (kokai) No. 10-242567).

However, employment of a conventional configuration in which a bottomportion of the electrode is caused to be in contact with a surface ofthe conductive n-type or p-type boron phosphide layer has failed tocompletely solve the problem that an electric current supplied fordriving the light-emitting device (i.e., device operation current) flowsin a short circuit manner into an underlying layer from the bottomportion of the electrode. Therefore, in an LED from which emitted lightis extracted to the outside via a boron phosphide crystal layer providedon a light-emitting layer so as to form an electrode, there arises aproblem of failure to attain diffusion of the device operation currentwidely in a light emission area. Thus, at present, an increase inemission intensity of a boron phosphide-based semiconductorlight-emitting device cannot be fully attained by increasing the lightemission area.

In order to overcome the aforementioned drawback involved in thebackground art, the present invention provides a configuration of a padelectrode for effectively diffusing a device operation current in a widerange of an emission area. Thus, an object of the present invention isto provide a boron phosphide-based semiconductor light-emitting devicehaving such a pad electrode. Another object of the invention is toprovide a production method for producing the boron phosphide-basedsemiconductor light-emitting device.

SUMMARY OF THE INVENTION

Accordingly, in order to attain the aforementioned objects, the presentinvention provides the following.

(1) A boron phosphide-based semiconductor light-emitting device,comprising:

a crystalline substrate;

a first semiconductor formed on said crystalline substrate, said firstsemiconductor layer including a light-emitting layer, serving as a baselayer and having a first region and a second region different from thefirst region;

a boron phosphide-based semiconductor amorphous layer formed on saidfirst region of said first semiconductor layer, said boronphosphide-based semiconductor amorphous layer including ahigh-resistance boron phosphide-based semiconductor amorphous layer;

a pad electrode formed on said high-resistance boron phosphide-basedsemiconductor amorphous layer for establishing wire bonding; and

a conductive boron phosphide-based crystalline layer formed on saidsecond region of said first semiconductor layer, said conductive boronphosphide-based crystalline layer extending optionally to a portion ofsaid boron phosphide-based semiconductor amorphous layer,

wherein said pad electrode is in contact with said boron phosphide-basedsemiconductor crystalline layer at a portion of said pad electrode abovethe bottom of said pad electrode.

(2) A boron phosphide-based semiconductor light-emitting device,comprising:

a crystalline substrate;

a first semiconductor layer formed on said crystalline substrate, saidfirst semiconductor layer including a light-emitting layer, serving as abase layer and having a first region and a second region different fromsaid first region;

a boron phosphide-based semiconductor amorphous layer formed on saidfirst region of said first semiconductor layer, said boronphosphide-based semiconductor amorphous layer including a first boronphosphide-based semiconductor amorphous layer having a conduction typeopposite to that of said first semiconductor layer;

a pad electrode formed on said first boron phosphide-based semiconductoramorphous layer, for establishing wire bonding; and

a conductive boron phosphide-based crystalline layer formed on saidsecond region of said first semiconductor layer, said conductive boronphosphide-based crystalline layer extending optionally to a portion ofsaid boron phosphide-based semiconductor amorphous layer,

wherein said pad electrode is in contact with said boron phosphide-basedsemiconductor crystalline layer at a portion of said pad electrode abovethe bottom of said pad electrode.

(3) A boron phosphide-based semiconductor light-emitting device asdescribed in the above (1) or (2), wherein said boron phosphide-basedsemiconductor amorphous layer has a multilayer structure formed from aboron phosphide-based semiconductor amorphous layer which is formed soas to attain contact with said first semiconductor layer and which is ofa conduction type opposite to that of said first semiconductor layer,and a high-resistance boron phosphide-based semiconductor amorphouslayer formed on said boron phosphide-based semiconductor amorphous layerhaving said opposite conduction type.

(4) A boron phosphide-based semiconductor light-emitting device asdescribed in any one of the above (1) to (3), wherein said boronphosphide-based semiconductor amorphous layer is formed of an undopedboron phosphide-based semiconductor.

(5) A boron phosphide-based semiconductor light-emitting device asdescribed in the above (3), wherein the two boron phosphide-basedsemiconductor amorphous layers constituting the multilayer structure ofsaid boron phosphide-based semiconductor amorphous layer are formed ofan undoped boron phosphide-based semiconductor.

(6) A boron phosphide-based semiconductor light-emitting device asdescribed in any one of the above (1) to (5), wherein said portion ofthe pad electrode which is in contact with said conductive boronphosphide-based semiconductor crystalline layer is formed of a materialable to form an Ohmic contact with said conductive boron phosphide-basedcrystalline layer.

(7) A boron phosphide-based semiconductor light-emitting device asdescribed in the above (6), wherein said portion of said pad electrodeformed of a material able to form an Ohmic contact with said conductiveboron phosphide-based crystalline layer extends to said conductive boronphosphide-based semiconductor crystalline layer.

(8) A boron phosphide-based semiconductor light-emitting device asdescribed in the above (6) or (7), wherein said pad electrode has abottom portion formed of a material able to form a non-Ohmic contactwith said boron phosphide-based semiconductor amorphous layer.

(9) A boron phosphide-based semiconductor light-emitting device asdescribed in any one of the above (1) to (8), wherein said pad electrodehas a bottom portion provided on said boron phosphide-basedsemiconductor amorphous layer, and an Ohmic electrode portion which isprovided on the bottom portion and which has a center coincident withthat of the plane shape of the bottom portion.

(10) A boron phosphide-based semiconductor light-emitting device asdescribed in the above (9), wherein said Ohmic electrode portion of saidpad electrode has a planar area greater than that of said bottom portionof said pad electrode.

(11) A boron phosphide-based semiconductor light-emitting device asdescribed in the above (10), wherein said Ohmic electrode portion ofsaid pad electrode extends to a surface of said conductive boronphosphide-based semiconductor crystalline layer.

(12) A boron phosphide-based semiconductor light-emitting device asdescribed in any one of (1) and (3) to (11) above, wherein saidhigh-resistance boron phosphide-based semiconductor amorphous layer hasa resistivity of 10 Ω·cm or more.

(13) A boron phosphide-based semiconductor light-emitting device asdescribed in (12) above, wherein said high-resistance boronphosphide-based semiconductor amorphous layer has a resistivity of 100Ω·cm or more.

(14) A boron phosphide-based semiconductor light-emitting device asdescribed in any one of (1) to (13) above, wherein said boronphosphide-based semiconductor is selected from the group consisting ofB_(α)Al_(β)Ga_(γ)In_(1-α-β-γ)P_(1-δ)As_(δ) (0<α≦1, 0≦β<1, 0≦γ<1,0<α+β+γ≦1, 0≦δ<1) and B_(α)Al_(β)Ga_(γ)In_(1-α-β-γ)P_(1-δ)N_(δ) (0<α≦1,0≦β<1, 0≦γ<1, 0<α+β+γ≦1, 0≦δ<1).

(15) A boron phosphide-based semiconductor light-emitting device as setforth in any one of (1) to (13) above, wherein said boronphosphide-based semiconductor is selected from the group consisting ofboron monophosphide (BP), boron gallium indium phosphide (compositionalformula: B_(α)Ga_(γ)In_(1-α-γ)P: 0<α≦1, 0≦γ<1), or a mixed-crystalcompound of boron nitride phosphide (compositional formula;BP_(1-δ)N_(δ); 0≦δ<1) or boron arsenide phosphide (compositionalformula: B_(α)P_(1-δ)As_(δ): 0≦δ<1).

(16) A boron phosphide-based semiconductor light-emitting device asdescribed in (6) above, wherein said conductive boron phosphide-basedcrystalline layer is a p-type conductivity layer and said portion ofsaid pad electrode in contact with said conductive boron phosphide-basedcrystalline layer is selected from the group consisting of Au—Zn andAu—Be.

(17) A boron phosphide-based semiconductor light-emitting device asdescribed in (6) above, wherein said conductive boron phosphide-basedcrystalline layer is an n-type conductivity layer and said portion ofsaid pad electrode in contact with said conductive boron phosphide-basedcrystalline layer is selected from the group consisting of Au—Ge, Au—Snand Au—In.

(18) A boron phosphide-based semiconductor light-emitting device asdescribed in (8) above, wherein said boron phosphide-based amorphouslayer is a p-type conductivity layer and said portion of said padelectrode in contact with said conductive boron phosphide-basedcrystalline layer is selected from the group consisting of Au—Ge, Au—Sn,Au—In, Ti, Mo, V, Ta, Hf and W.

(19) A boron phosphide-based semiconductor light-emitting device asdescribed in (8) above, wherein said boron phosphide-based amorphouslayer is a p-type conductivity layer and said portion of said padelectrode in contact with said conductive boron phosphide-basedcrystalline layer is selected from the group consisting of Au—Zn, Au—Be,Au—In, Ti, Mo, V, Ta, Hf and W.

(20) A method for producing a boron phosphide-based semiconductorlight-emitting device, comprising:

forming a semiconductor layer including a light-emitting layer on acrystalline substrate through vapor phase growth;

depositing, through vapor phase growth, employing said firstsemiconductor layer serving as a base layer, at a crystalline substratetemperature falling within a range of 250° C. to 1,200° C., a boronphosphide-based semiconductor amorphous layer having high resistance ora boron phosphide-based semiconductor amorphous layer having aconduction type opposite to that of the base layer;

selectively removing said boron phosphide-based semiconductor amorphouslayer, thereby causing said boron phosphide-based semiconductoramorphous layer to remain in a first region and exposing said firstsemiconductor layer in a second region different from said first region;

depositing a conductive boron phosphide-based semiconductor crystallinelayer on said exposed first semiconductor layer and said boronphosphide-based semiconductor amorphous layer through vapor phase growthat a crystalline substrate temperature falling within a range of 750° C.to 1,200° C.;

selectively removing said conductive boron phosphide-based semiconductorcrystalline layer in said first region, thereby exposing said boronphosphide-based semiconductor amorphous layer;

forming a pad electrode for establishing wire bonding on said exposedboron phosphide-based semiconductor amorphous layer such that said padelectrode is caused to be in contact with said boron phosphidecrystalline layer; and

subsequently, cutting said formed structure, to thereby produceindividual light-emitting devices.

(21) A method for producing a boron phosphide-based semiconductorlight-emitting device as described in the above (20), further comprisingremoving said conductive boron phosphide-based semiconductor crystallinelayer present in said first region where said pad electrode is to beprovided and simultaneously, removing said conductive boronphosphide-based semiconductor crystalline layer present in a regionwhere a stripe-like dicing line for cutting and separating the structureinto individual light-emitting devices is provided, thereby exposing asurface of the underlying boron phosphide-based semiconductor amorphouslayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of the LED mentioned inExample 1.

FIG. 2 is a schematic plane view of the LED mentioned in Example 2.

FIG. 3 is a schematic cross-sectional view of the LED mentioned inExample 2.

BEST MODES FOR CARRYING OUT THE INVENTION

The boron phosphide-based semiconductor forming the amorphous layer andthe conductive crystalline layer refers to a semiconductor containingboron (symbol of element: B) and phosphorus (symbol of element: P).

Specific examples include B_(α)Al_(β)Ga_(γ)In_(1-α-β-γ)P_(1-δ)As_(δ)(0<α≦1, 0≦β<1, 0≦γ<1, 0<α+β+γ≦1, 0≦δ<1) andB_(α)Al_(β)Ga_(γ)In_(1-α-β-γ)P_(1-δ)N_(δ) (0<α≦1, 0≦β<1, 0≦γ<1,0<α+β+γ≦1, 0≦δ<1). More specifically, the semiconductor is boronmonophosphide (BP), boron gallium indium phosphide (compositionalformula: B_(α)Ga_(γ)In_(1-α-γ)P: 0<α≦1, 0≦γ<1), or a mixed-crystalcompound containing a plurality of Group V element species such as boronnitride phosphide (compositional formula: BP_(1-δ)N_(δ): 0≦δ<1) or boronarsenide phosphide (compositional formula: B_(α)P_(1δ)As_(δ): 0≦δ<1). Inparticular, boron monophosphide (BP) is an essential constituent ofboron phosphide-based semiconductor mixed-crystals. When BP, having aband gap at room temperature as wide as 2.8 to 3.4 eV, is employed as anessential constituent, a boron phosphide-based amorphous or crystallinelayer having a wide band gap can be formed. When a boron phosphide-basedcrystalline layer having a band gap of 3.0 eV is used, there can besuitably formed a barrier layer in a light-emitting portion including aGroup III nitride semiconductor having a band gap of, for example, 2.7eV, or a window layer which permits transmission of emitted light to theoutside.

The amorphous or crystalline boron phosphide-based semiconductor layercan be formed through use of vapor phase growth means such as thehalogen method (see “Journal of the Japanese Association for CrystalGrowth,” Vol. 24, No. 2, (1997), p. 150), the hydride method (see J.Crystal Growth, 24/25 (1974), p. 193-196), or molecular beam epitaxy(see J. Solid State Chem., 133 (1997), p. 269-272). Alternatively, thesemiconductor layer can be vapor-phase grown through metal-organicchemical vapor deposition (MOCVD) (see Inst. Phys. Conf. Ser. No. 129(IOP Publishing Ltd. (UK, 1993), p. 157-162). Among them, MOCVD is aparticularly advantageous means for vapor-phase growing an amorphouslayer at lower temperature, because a readily decomposable substancesuch as triethylboran (chemical formula: (C₂H₅)₃B) is employed as aboron source. When an amorphous layer formed of a boron phosphide-basedsemiconductor is formed through use of any of these vapor phase growthmeans, the growth temperature is preferably controlled to 1,200° C. orlower. When the growth temperature is higher than 1,200° C., growth ofthe amorphous boron phosphide-based semiconductor layer yielded fromboron monophosphide (BP) is inhibited due to generation of polyboronspecies such as B₁₃P₂. From another aspect, the growth temperature ispreferably controlled to 250° C. or higher, because sources of elementsforming the amorphous boron phosphide-based semiconductor layer(constitutional elements) can be thermally decomposed sufficiently inthe vapor phase growth zone, thereby promoting layer formation. Ingeneral, when a vapor phase growth temperature higher than 1,000° C. isemployed, such an amorphous or crystalline semiconductor layer having ap conduction type tends to be formed, whereas a similar amorphous orcrystalline semiconductor layer having an n conduction type is formed ata growth temperature lower than 1000° C.

In order to effectively form the amorphous boron phosphide-basedsemiconductor layer through use of the aforementioned vapor phase growthmeans, the so-called V/III ratio is essentially controlled so as to fallwithin a range of 0.2 to 50. The V/III ratio can be represented by aratio of total Group V element concentration to total Group III elementconcentration, these elements being fed into a zone (growth zone) wheregrowth of the boron phosphide-based semiconductor layer is performed.When the V/III ratio is controlled to a very low level; i.e., less than0.2, spherical boron (B)-rich grains are generated in a considerableamount, thereby undesirably failing to successfully obtain an amorphouslayer having a flat surface, whereas when the V/III ratio is in excessof 50, an undesirable polycrystalline boron phosphide-basedsemiconductor layer may be formed. Both cases are not suited forsuccessfully forming an amorphous layer. In the present invention, theterm “crystalline layer” refers to any of a layer formed of a singlecrystal, a polycrystalline layer formed of an amorphous portion and asingle-crystal portion, and a polycrystalline layer containing singlecrystals having crystalline orientations which differ from one another.The boron phosphide-based crystalline layer can be successfully formedat a V/III ratio of 100 or higher, more preferably 500 to 2,000. Whenthe V/III ratio is higher than 2,000, deposits containing Group Velements such as phosphorus are generated, resulting in difficulty inprovision of a flat-surface boron phosphide-based semiconductorcrystalline layer, which is not preferred. Whether the formed layer isamorphous, polycrystalline, or a single crystal can be determinedthrough general electron-beam diffraction or X-ray diffractiontechniques.

The boron phosphide-based semiconductor amorphous layer formed on avapor-phase grown semiconductor layer serving as a base layer ispreferably fabricated from a high-resistance amorphous layer having alarge resistivity; an amorphous layer which is of a conduction typeopposite to (converse to) that of the semiconductor layer serving as thebase layer; or a multilayer structure formed of the amorphous layers.The high-resistance amorphous layer preferably has a resistivity at roomtemperature of 10 Ω·cm or higher, more preferably 102 Ω·cm or higher.The expression “of a conduction type opposite to that of the base layer”refers to, for example, a p-type when the base layer is of an n-type.The amorphous layer is preferably formed on, for example, alight-emitting layer formed of gallium indium nitride (compositionalformula: Ga_(x)In_(1-x)N: 0≦x≦1) or a cladding barrier layer formed ofaluminum gallium nitride (compositional formula; Al_(x)Ga_(1-x)N:0≦x≦1), serving as the base layer. For the sake of convenience, theamorphous layer having a high resistance is referred to as a“high-resistance amorphous layer,” and the amorphous layer which is of aconduction type opposite to that of the base layer is referred to as an“opposite conduction type amorphous layer.” An essential requirement isthat either a high-resistance amorphous layer or an opposite conductiontype amorphous layer is provided under the bottom of a pad electrode,which is disposed above the light-emitting layer or the barrier layer;i.e., is provided in the projection area of the pad electrode. In astructure in which a pad electrode is provided on a high-resistanceamorphous layer such that the bottom of the pad electrode is in contactwith the amorphous layer, the high-resistance amorphous layer serves asa resistor which inhibits a flow of device operation current from thebottom of the pad electrode into the underlying light-emitting layer ina short circuit manner. In a structure in which a pad electrode isprovided on an amorphous layer which is of an opposite conduction typeto that of the base layer such that the bottom of the pad electrode isin contact with the amorphous layer, the conductive amorphous layerforms a pn junction structure with the base layer and inhibits flow ofdevice operation current from the bottom of the pad electrode into theunderlying light-emitting layer in a short circuit manner. The areawhere the high-resistance amorphous layer or the opposite conductiontype amorphous layer (a first area) is to be formed is not necessarilyidentical with the area where the bottom of the pad electrode is formed(a third area), and the first area is effective so long as the areaincludes at least a portion of the bottom of the pad electrode (theprojection area of the pad electrode). However, the opposite conductiontype amorphous layer which forms a pn junction for inhibiting deviceoperation current or the high-resistance amorphous layer is preferablyprovided in an area limited to the projection area of the pad electrodeor to an area around the projection area. When the high-resistanceamorphous layer or the opposite conduction type amorphous layer isformed in the projection area of the pad electrode, device operationcurrent from the bottom of the pad electrode into the underlyinglight-emitting layer in a short circuit manner is prevented, wherebylight emission occurring in an area of the light-emitting layer coveredwith the pad electrode can be prevented. On the other hand, in order toattain sufficient and uniform flow of device operation current in thebase layer, the conductive crystalline layer formed in an area differentfrom the aforementioned first area (a second area) is preferably incontact with the base semiconductor layer over a wide range. If thehigh-resistance amorphous layer or the opposite conduction typeamorphous layer is provided over a wide range in the area (second area)different from the projection area of the pad electrode; for example, onthe entire surface of the light-emitting layer, a device operationcurrent cannot flow sufficiently and uniformly in the light-emittinglayer, thereby preventing production of a high-emission-intensity LED.

Furthermore, when the boron phosphide-based semiconductor amorphouslayer is fabricated by stacking an high-resistance amorphous layer andan amorphous layer which is of a conduction type opposite to that of thebase layer, flow of the aforementioned device operation current in ashort circuit manner is more effectively prevented. Preferably, anopposite conduction type amorphous layer is provided on the base layer,and then a high-resistance amorphous layer is formed on the oppositeconduction type amorphous layer, because a flow of device operationcurrent into a junction portion of the pn junction between the oppositeconduction type amorphous layer and the base layer can be effectivelydecreased by the mediation of the high-resistance amorphous layer.

In an area where the bottom portion of the pad electrode is provided,the high-resistance amorphous layer suitably has a thickness of 2 nm ormore, so as to uniformly cover the surface of the base layer with theamorphous layer. The opposite conduction type amorphous layer preferablyhas a thickness of 50 nm or more, so as to inhibit passage of carriers,through the tunnel effect, to the base layer. A thickness of thehigh-resistance amorphous layer or the opposite conduction typeamorphous layer in excess of 200 nm is not preferred, because thedifference in level between the Ohmic electrode mentioned hereafter andthe surface of the boron phosphide-based semiconductor crystalline layerincreases, thereby inhibiting formation of an electrode having excellentbonding performance to the boron phosphide-based semiconductorcrystalline layer.

A pad electrode whose bottom is in contact with an opposite conductiontype amorphous layer or a high-resistance amorphous layer may be formedin the following manner. Firstly, the opposite conduction type amorphouslayer or the high-resistance amorphous layer is grown on the base layer,followed by selective removal of a portion of the opposite conductiontype amorphous layer or a portion of the high-resistance amorphous layerwhich is present in the first area including an area where a padelectrode is formed. Secondly, a conductive boron phosphide crystallinelayer is grown, and a portion of the conductive boron phosphide-basedcrystalline layer which is present in the area where the pad electrodeis formed is removed, thereby exposing a surface of the oppositeconduction type amorphous layer or the high-resistance amorphous layer.Thereafter, on the thus-exposed surface of the amorphous layer, amaterial which suitably forms the bottom of the pad electrode isdeposited. The boron phosphide-based amorphous layer and the boronphosphide-based crystalline layer can be removed through etching; forexample, by a conventional chlorine (symbol of element: Cl) plasmaetching technique. In order to leave the opposite conduction type orhigh-resistance amorphous layer selectively in an area under the padelectrode, a conventional photolithographic technique can be employed.In a limited surface region where the pad electrode is provided, thebottom of the pad electrode is preferably provided through a selectivepatterning technique based on the conventional photolithographictechnique. Even when the pad electrode is formed such that the bottomthereof is in contact with any of the surface of the opposite conductiontype or high-resistance amorphous layer, the bottom portion can inhibita flow of device operation current in a short circuit manner to aportion of the underlying light-emitting layer corresponding to theprojection area of the bottom portion. In addition, device operationcurrent can be supplied preferentially to a light emission area otherthan the projection area of the pad electrode which intercepts lightemission to the outside. Thus, such a configuration is suitable forproducing, for example, a high-emission-intensity LED.

When the amorphous layer is formed from a layer to which no impurity hasbeen intentionally added; i.e., an undoped layer, electrical orcrystallographic undesirable modification of the light-emitting layer orthe barrier layer serving as a base layer is effectively prevented. In aconventional stacked structure in which a gallium nitride (GaN) layerintentionally doped with magnesium (symbol of element: Mg) is providedon an n-type light-emitting layer, an increase in resistance of thelight-emitting layer caused by thermal diffusion of magnesium (Mg)serving as a p-type impurity can be prevented through provision of suchan undoped layer. In a light-emitting layer included in a quantum wellstructure, provision of such an undoped layer can prevent an increase inthe degree of disorder of the heterojunction interface between thebarrier layer and the well layer. The conductivity of a boronphosphide-based semiconductor amorphous layer can be regulated bymodifying vapor phase growth temperature (growth temperature) at whichthe layer is formed and the V/III ratio. By employing a low growthtemperature and a low V/III ratio, an amorphous layer having a higherresistivity can be produced. When the vapor phase growth is performed ata high V/III ratio and at high temperature, an amorphous layer having alower resistance can be formed. The resistivity—index of conductivity—ofthe boron phosphide-based semiconductor amorphous layer can bedetermined through conventional Hall effect measurement.

In addition to the effect of the opposite conduction type orhigh-resistance amorphous layer on prevention of flow of operationcurrent in a short circuit manner, when the bottom portion of the padelectrode is formed of a material able to form non-Ohmic contact with aboron phosphide-based semiconductor, the effect on prevention of flow ofoperation current in a short circuit manner can be further enhanced. Theterm “non-Ohmic contact” refers to electric contact involving arectification characteristic as shown in the case of Schottky contact.In the present invention, the non-Ohmic contact also encompasses anelectric contact with a contact resistance higher than 1×10⁻³ Ω·cm. Thematerial for forming the bottom portion of the pad electrode varies inaccordance with the conduction type of the boron phosphide-basedsemiconductor amorphous layer. When the boron phosphide-basedsemiconductor amorphous layer has high resistance and is of a pconduction type, the bottom portion is formed from a gold alloy such asgold (symbol of element: Au)-germanium (symbol of element: Ge), gold(Au)-tin (symbol of element: Sn), or gold (Au)-indium (symbol ofelement: In). With respect to an n-type boron phosphide-basedsemiconductor amorphous layer, the bottom portion is formed from a goldalloy such as gold (Au)-zinc (symbol of element: Zn) or gold(Au)-beryllium (symbol of element: Be). Regardless of the conductiontype of the amorphous layer, a bottom portion having a rectificationcharacteristic can be formed from transition metal. Examples oftransition metal material having a Schottky rectification characteristicinclude titanium (symbol of element: Ti), molybdenum (symbol of element:Mo), vanadium (symbol of element: V), tantalum (symbol of element: Ta),hafnium (symbol of element: Hf), and tungsten (symbol of element: W).

On the film serving as the bottom portion which has been provided so asto attain contact with the surface of the boron phosphide-basedsemiconductor amorphous layer, there is provided an Ohmic electrodeformed of a material able to form Ohmic contact with the boronphosphide-based semiconductor crystalline layer. The material forforming the Ohmic electrode is selected in accordance with theconduction type of the boron phosphide-based semiconductor crystallinelayer. The p-type boron phosphide-based semiconductor crystalline layercan be formed from a gold alloy such as gold-zinc or gold-beryllium. Then-type boron phosphide-based semiconductor crystalline layer can beformed from a gold alloy such as gold-germanium, gold-tin, orgold-indium. When the boron phosphide-based semiconductor amorphouslayer on which the bottom portion of the pad electrode is provided andthe boron phosphide-based semiconductor crystalline layer on which theOhmic electrode is provided are layers having conduction types differingfrom each other, the bottom portion of the pad electrode and the Ohmicelectrode provided on the bottom portion can be formed from the samematerial. For example, when the bottom portion of the pad electrode isprovided so as to attain contact with the p-type boron phosphide-basedsemiconductor amorphous layer and the Ohmic electrode is provided so asto attain contact with the n-type boron phosphide-based semiconductorcrystalline layer, to thereby form the pad electrode, both the bottomportion and the Ohmic electrode are formed from a gold-germanium alloy.It is not preferred that both the Schottky rectifying electrode and theOhmic electrode are formed from niobium (symbol of element: Nb),chromium (symbol of element: Cr), or the aforementioned transitionmetal.

An Ohmic electrode which is closely bonded with the boronphosphide-based semiconductor crystalline layer can be formed bycontrolling the bottom area of the bottom portion so as to exceed theplanar area of the pad electrode and causing a portion providing aplanar area exceeding the bottom area to extend to the surface of theboron phosphide-based semiconductor crystalline layer. Specifically, abottom portion including the bottom surface which is formed so as toattain contact with the boron phosphide-based semiconductor amorphouslayer is formed, and subsequently, a material for forming the Ohmicelectrode is provided so as to attain contact with the bottom portionand with the boron phosphide-based semiconductor crystalline layer. Thethus-provided Ohmic electrode material is processed through aconventional photolithographic technique such that the formed electrodehas a diameter greater than that of the bottom surface when the bottomsurface is, for example, of circular shape. In this case, a portion ofthe Ohmic electrode present outside the circular portion correspondingto the bottom is caused to be in close contact with the surface of theboron phosphide-based semiconductor crystalline layer. The plane shapeof the bottom portion and that of the Ohmic electrode are notnecessarily similar to each other. For example, the bottom portion mayhave a circular plane shape, and the Ohmic electrode may have a squareplane shape. However, it is particularly preferred that the center ofthe plane shape of the bottom portion and that of the plane shape of theOhmic electrode generally coincide with each other for producing a padelectrode which is bonded to the boron phosphide-based semiconductorcrystalline layer with in-plane isotropy in bonding strength.

Another Ohmic electrode is preferably formed such that the electrode isin electrical contact with the Ohmic electrode which is in close contactwith the boron phosphide-based semiconductor crystalline layer and iscaused to extend to a surface of the boron phosphide-based semiconductorcrystalline layer, because device operation current can be distributedto a light-emission area other than the projection area of the padelectrode. In other words, in an LED from which emitted light isextracted via the boron phosphide-based semiconductor crystalline layerto the outside, device operation current can be diffused over the planeof a light-emission area which is not covered with the pad electrode andfrom which emitted light is suitably extracted to the outside. Thethus-extending Ohmic electrode effectively diffuses, over a wide area ofthe light-emission area, the device operation current which can beinhibited from flowing in a short circuit manner by the bottom of thepad electrode to a portion of the light-emitting layer present in theprojection area of the pad electrode, thereby attaining production of ahigh-emission-intensity LED. The Ohmic electrode provided so as toextend a surface of the boron phosphide-based semiconductor crystallinelayer can be formed from a material differing from the Ohmic materialincluded in the pad electrode. For example, the Ohmic electrode includedin the pad electrode is formed from a gold-germanium alloy, and theOhmic electrode which extends to the surface is formed from a gold-tinalloy. The Ohmic electrode which extends to the surface is morepreferably formed of an alloy containing a Group IV element such as tin(Sn) or germanium (Ge) rather than a Group III element such as gallium(Ga) or indium (In), from the viewpoint of close bonding with the boronphosphide-based semiconductor crystalline layer. When the pad electrodeand the Ohmic electrode which extends to the surface are formed from thesame material, the two electrodes can be formed simultaneously, therebyattaining production of a boron phosphide-based semiconductorlight-emitting device through simple processes.

The Ohmic electrode which extends to the surface is preferably placedsuch that the device operation current can be distributed entirely anduniformly over the light-emission area other than the projection area ofthe pad electrode. In other words, the Ohmic electrode is preferablyplaced such that a uniform electric potential distribution can beattained on the surface of the boron phosphide-based semiconductorcrystalline layer, furthermore on the surface of the light-emittinglayer. The Ohmic electrode which extends to the surface can be formed ofa stripe, circle, or frame form electrode which is in electrical contactwith the pad electrode. These electrodes, such as a stripe formelectrode and a frame form electrode, can be combined so as to establishelectric contact with the pad electrode. A line electrode for formingthe stripe, circle, or frame form electrode generally has a line widthof 10 μm or more, more preferably 20 μm or more, so as to preventbreakage upon increase in device operation current flow. Throughconventional photolithography, patterning, and selective etchingtechniques, an electrode having a desired shape and line width can beprovided on the surface of the boron phosphide-based semiconductorcrystalline layer.

The boron phosphide-based semiconductor light-emitting device isproduced by forming a pad electrode or an Ohmic electrode attached tothe pad electrode, and subsequently cutting the semiconductor elementinto individual devices. The cutting to form individual devices isperformed through employment of grooves in the form of a straight line,which are generally provided along a cleavage direction of a crystalserving as the substrate and which are generally called cutting lines,scribe lines, or dicing lines. According to the present invention, asmentioned above, the pad electrode is provided such that the bottomportion thereof is in contact with the boron phosphide-basedsemiconductor amorphous layer. Thus, a portion of the boronphosphide-based semiconductor crystalline layer corresponding to an areawhere the bottom portion is provided must be removed. In addition, whengrooves serving as cutting lines for producing individual devices areformed, steps of producing the boron phosphide-based semiconductorlight-emitting device can be simplified. Therefore, in the presentinvention, a surface of the amorphous layer is exposed in an area wherethe bottom portion of the pad electrode is provided and a surface of theboron phosphide-based semiconductor amorphous layer is exposed in anarea where cutting lines are provided, thereby forming grooves forcutting a semiconductor element. When a cubic zincblende crystal is usedas a substrate, the cutting grooves are advantageously provided along<110> crystalline directions, which are cleavage directions and arenormal to each other. Each cutting groove (cutting line) is preferablyof a sufficient width so as to prevent severe damage of the boronphosphide-based semiconductor crystalline layer serving as a groove sidecaused by contact with the cutting edge of a cutting tool. Generally,the width preferably falls within a range of 40 μm to 70 μm. When thecutting line has a width in excess of 70 μm, the cutting line isunnecessarily broad, and an excessively wide space is provided for thecutting edge of the cutting tool. Therefore, the cut edge tends todeviate from a straight line, causing difficulty in production ofindividual devices having smooth cut surfaces.

The high-resistance boron phosphide-based semiconductor amorphous layeror the boron phosphide-based semiconductor amorphous layer having aconduction type opposite to that of the base layer which is providedunder the bottom surface of the pad electrode inhibitsshort-circuit-like flow of device operation current supplied via thebottom of the pad electrode provided thereon into the underlyinglight-emitting layer.

The bottom surface of the pad electrode which is formed from a materialable to form non-Ohmic contact with the boron phosphide-basedsemiconductor prevents short-circuit-like flow of device operationcurrent supplied via the pad electrode into the underlying boronphosphide-based semiconductor amorphous layer.

The Ohmic electrode which is provided so as to attain contact with thebottom portion included in the pad electrode; which has a planar areagreater than that of the bottom portion; and which is provided so as toattain contact with a surface of the boron phosphide-based semiconductorcrystalline layer provides a pad electrode closely bonding to the boronphosphide-based semiconductor layer.

The Ohmic electrode which is provided so as to attain electric contactwith another Ohmic electrode included in the pad electrode and whichextends to a surface of the boron phosphide-based semiconductorcrystalline layer distributes device operation current over a wide rangeof the light-emission area.

EXAMPLES Example 1

The boron phosphide-based compound semiconductor light-emitting deviceaccording to the present invention will next be described in detail,taking as an example a light-emitting diode (LED) employing a padelectrode having a bottom surface which is in contact with ahigh-resistance boron phosphide amorphous layer. FIG. 1 schematicallyshows the cross-section of a stacked structure 11 employed forfabricating an LED 10 having a double-hetero (DH) structure.

A phosphorus (P)-doped n-type silicon (Si) single crystal was used as asubstrate 101. On the surface of the substrate 101, a lower claddinglayer 102 formed of n-type boron phosphide (BP) was deposited throughuse of atmospheric pressure (near atmospheric pressure) metal-organicvapor phase epitaxy (MOVPE) means. The lower cladding layer 102 wasdeposited at 950° C. by use of a triethylboran (molecular formula:(C₂H₅)₃B) as a boron (B) source and phosphine (molecular formula: PH₃)as a phosphorus source. The carrier concentration of the undoped n-typeBP layer serving as the lower cladding layer 102 was found to be 1×10¹⁹cm⁻³, and the thickness of the layer was controlled to 420 nm.

On the n-type lower cladding layer 102, a light-emitting layer 103formed of n-type gallium indium nitride (Ga_(0.90)In_(0.10)N) wasvapor-grown through atmospheric pressure MOCVD at 825° C. The galliumindium nitride layer serving as a well layer 103 had a multi-phasestructure which was formed from a plurality of gallium indium nitridedomains having indium compositional proportions that differ from oneanother. The average compositional proportion of In was found to be 0.10(=10%). The thickness of the well layer 103 was controlled to 10 nm. Onthe light-emitting layer 103, a silicon (Si)-doped n-type galliumnitride (GaN) layer 104 was provided through use of atmospheric pressureMOCVD means, at 825° C., by use of trimethylgallium (molecular formula:(CH₃)₃Ga)/NH₃/H₂ reaction system so as to attain joining to thelight-emitting layer. The thickness of the GaN layer 104 was controlledto 20 nm. The n-type GaN layer 104 was provided in order to form, in aninner region of the light-emitting layer 103 in the vicinity of thejunction interface, a band structure in which a conduction band and avalence band are bent.

On the n-type GaN layer 104, an undoped boron phosphide (BP) amorphouslayer 105 was provided. The boron phosphide amorphous layer 105 wasprovided through use of atmospheric pressure MOCVD means employing a(C₂H₅)₃B/PH₃/H₂ reaction system. As the amorphous layer 105 wasvapor-phase grown at 550° C. and a v/III ratio (=PH₃/C₂H₅)₃B) of 10, ahigh-resistance amorphous layer having a resistivity of 10 Ω·cm at roomtemperature was produced. The thickness of the undoped amorphous layer105 was controlled to 15 nm. Subsequently, through conventionalselective patterning and plasma etching techniques, a portion of theamorphous layer 105 was left exclusively in an area where a padelectrode 107 was to be formed. The remained amorphous layer 105 was acircular area having a diameter of 120 μm. Other than the portion of theremained amorphous layer, the amorphous layer 105 was removed throughetching, thereby exposing the surface of the n-type GaN layer 104.

Subsequently, through use of the same atmospheric-pressure MOCVD meansemploying a (C₂H₅)₃B/PH₃/H₂ reaction system and by use of the same vaporphase growth apparatus, a p-type boron phosphide crystalline layer 106was provided so as to attain joining to the remained amorphous layer 105and the exposed surface of the n-type GaN layer 104. The undoped boronphosphide crystalline layer 106 was provided at 1,025° C., which washigher than the amorphous layer 105 growth temperature. As the boronphosphide crystalline layer 106 was vapor-phase grown at a V/III ratioof 1,300, the carrier concentration of the layer was found to be 2×10¹⁹cm⁻³. The thickness of the layer was controlled to 580 nm. The boronphosphide crystalline layer 106 had a band gap of 3.2 eV at roomtemperature. Therefore, the boron phosphide crystalline layer 106 wasemployed as a p-type upper cladding layer also serving as a window layerthrough which emitted light is transmitted to the outside.

Through employment of a conventional photolithography technique, thecenter of the surface of the boron phosphide crystalline layer 106serving as the p-type upper cladding layer was selectively patterned,thereby providing a circular plane serving as an area for providing thepad electrode 107. In addition, an area 108 for providing a cuttinggroove was selectively patterned, thereby providing a stripe-shapeplane. Thereafter, exclusively within the thus-patterned area, the boronphosphide crystalline layer 106 provided on the amorphous layer 105 wasselectively removed through the plasma etching method employing argon(Ar)/methane (molecular formula: CH₄)/H₂ gas mixture. Through theetching, the portion of the surface of the boron phosphide amorphouslayer 105 corresponding to the circular planer area (diameter: 100 μm)for providing the pad electrode 107 was exposed. In addition, within thestripe-shape area 108 having a width of 50 μm serving as a cutting line,the surface of the boron phosphide crystalline layer 105 was alsoexposed. The stripe-shape area 108 serving as a cutting line wasprovided in a direction parallel to a cleavage direction of the Sisingle-crystal substrate 101; i.e., the <110> crystalline direction.Another cutting line was provided in a direction normal to the <110>crystalline direction.

Next, through employment of a photoresist mask which had beenselectively patterned so as to exclusively open the area for providingthe pad electrode 107, a gold-germanium (Au 95 wt. %, Ge 5 wt. %) alloyfilm serving as a bottom portion 107 a of the pad electrode 107 wasdeposited through a conventional vacuum vapor deposition technique.Subsequently, the mask was peeled off from the surface of the boronphosphide crystalline layer 106, thereby removing the Au—Ge filmdeposited on the mask. The thickness of the Au—Ge film remainingexclusively in the area of the pad electrode 107 and serving as a bottomportion of the pad electrode was controlled to 150 nm. Subsequently, thesurface of the boron phosphide crystalline layer 106 was coated with aphotoresist, and the layer was selectively patterned, to thereby providea circular opening (diameter: 150 μm) exclusively in the areacorresponding to that for providing an Ohmic electrode 107 b of the padelectrode 107. The center of the thus-formed opening and the center ofthe plane shape of the aforementioned bottom portion 107 a were causedto coincide. Then, a gold-beryllium (Au 99 wt. %, Be 1 wt. %) alloy filmwas deposited through a conventional vacuum vapor deposition technique,to thereby form the Ohmic electrode 107 b which attained Ohmic contactwith the p-type boron phosphide crystalline layer 106. The thickness ofthe Ohmic electrode 107 b was controlled to 800 nm. The portion of theAu—Be alloy film deposited on the mask, except the portion of the maskcorresponding to the Ohmic electrode 107 b for forming the pad electrode107, was peeled off. Thus, the ohmic electrode 107 b having a planararea larger than that of the bottom portion 107 a and serving as theupper portion of the pad electrode 107 which was in contact with thesurface of the p-type boron phosphide crystalline layer 106 was formed.

On the backside of the silicon single-crystal substrate 101, an n-typeOhmic electrode 109 formed of an aluminum (Al)-antimony (Sb) alloy wasprovided. By peeling of the mask for providing the pad electrode 107 inthe center of the boron phosphide crystalline layer 106, a portion ofthe boron phosphide amorphous layer 105 formed in advance on thestrip-shape cutting area 108 was exposed. A diamond blade was moved inthe straight line while being held in contact with the surface of theboron phosphide amorphous layer 105 along the strip-shape cutting area108; i.e., the cutting line, whereby individual LEDs 10 in the form ofsquare shape having a side length (equal to intervals between two centerlines of the cutting lines 108) of 300 μm were produced. As the width ofeach cutting line 108 was adjusted to a value about 2.5 times that ofthe blade (about 20 μm), each separated LED 10 had a flat side surface.

Observation through a conventional cross-sectional TEM techniquerevealed that the boron phosphide amorphous layer 105 exhibited a haloelectron-beam diffraction pattern in a restricted field. In contrast, inthe electron-beam diffraction pattern of the boron phosphide crystallinelayer 106, diffraction spots appearing on the diffraction ring wereobserved more often than those observed in the case of thesingle-crystal layer, indicating that the boron phosphide crystallinelayer was formed of a polycrystalline layer.

According to the present invention, a ceiling portion of the Ohmicelectrode 107 b having a plate area greater than that of the bottomportion 107 a was provided so as to attain contact with the surface ofthe p-type boron phosphide crystalline layer 106. Therefore, no peelingof the pad electrode 107 was observed during wire bonding. Emissioncharacteristics of each LED was confirmed upon passage of deviceoperation current of 20 mA in the forward direction between the padelectrode 107 and the n-type Ohmic electrode 109, with these twoelectrode being firmly bonded. The LED 10 emitted blue light having anemission center wavelength of 440 nm, with a half-width value observedin the emission spectrum of 280 meV. Luminous intensity of the LED chipbefore resin-molded as determined through a conventional photometricsphere was 7 mcd. Furthermore, emission with uniform intensity wasprovided from virtually the entire portion of the emission area otherthan the projection area of the pad electrode 107, because the lowerbottom portion 107 a of the p-type Ohmic electrode 107 b was provided soas to attain contact with the surface of the high-resistance boronphosphide amorphous layer 105, thereby distributing the device operationcurrent over a wide area of the light-emitting area 103. The forwardvoltage at a forward current of 20 mA was found to be 3.5 V and thereverse voltage at a reverse current of 10 μA was found to be 8.2 V.

Example 2

The boron phosphide-based compound semiconductor light-emitting deviceaccording to the present invention will next be described in detail,taking as an example a double-heterojunction (DH) light-emitting diode(LED) employing a pad electrode having a bottom surface which is incontact with the surface of a boron phosphide amorphous layer of amulti-layer structure.

FIG. 2 is a schematic plane view of the LED 12 according to Example 2.FIG. 3 schematically shows a cross-section of the LED 12 taken along thebroken line A-A′ shown in FIG. 2. In FIGS. 2 and 3, the same members asshown in FIG. 1 are denoted by the same reference numerals.

On an n-type GaN light-emitting layer 104 which had been formed in thesame manner as described in Example 1, an undoped p-type boron phosphideamorphous layer 201 was formed. The carrier concentration and thethickness of the p-type boron phosphide amorphous layer 201 werecontrolled to 8×10¹⁸ cm⁻³ and 12 nm, respectively. On the p-type boronphosphide amorphous layer 201, an undoped high-resistance boronphosphide layer 105 was stacked. The resistivity and the thickness ofthe undoped high-resistance boron phosphide layer 105 were controlled to10 Ω·cm at room temperature and 12 nm, respectively. Through aconventional photolithography technique, a portion of the p-type boronphosphide amorphous layer 105 and a portion of the high-resistance boronphosphide amorphous layer 201 were left exclusively in an area where apad electrode 107 was to be formed.

The p-type and high-resistance amorphous layers 105 and 201 were leftsuch that circular planes having a diameter of 120 μm were stacked, withthe centers of the plane being caused to coincide. Subsequently, anundoped p-type boron phosphide crystalline layer 106 as described inExample 1 was deposited on the high-resistance boron phosphide amorphouslayer 105. The p-type boron phosphide crystalline layer 106 wasselectively removed through plasma etching exclusively in areas forproviding the pad electrode 107 and a cutting line 108, thereby exposingthe surface of the high-resistance boron phosphide amorphous layer 105.The planer area provided by removing the p-type boron phosphidecrystalline layer 106 was in the form of a circle having a diameter of150 μm. The center of the circle and that of the circular plane of theleft high-resistance boron phosphide amorphous layer 105 were caused tocoincide. Subsequently, the pad electrode 107 having a bottom portion107 a (molybdenum (Mo)) being in contact with the surface of thehigh-resistance amorphous surface 105 and an upper Ohmic electrode 107 b(gold-beryllium (Au—Be)) was formed. The thickness of the molybdenum(Mo) layer and that of the Au—Be layer were controlled to 10 nm and 700nm, respectively. As shown in FIG. 3, a circular electrode and a stripeform electrode serving as an additional Ohmic electrode 107 c wereattached, so as to establish electric contact, to the Au—Be Ohmicelectrode 107 b serving as a ceiling portion of the pad electrode 107.

In a manner as described in Example 1, cutting was performed along thecutting lines 108 provided in parallel to the crystalline directions ofthe Si single-crystalline substrate 101 of {1.−1.0} and {−1.−1.0},whereby individual LEDs 12 in the form of square shape having a sidelength of 350 μm were produced. Upon passage of device operation currentof 20 mA in the forward direction, the emitted light had an emissioncenter wavelength of 440 nm, which was approximately equivalent to thatof the LED 10 of Example 1. The luminous intensity of the LED chip asdetermined through a conventional photometric sphere was 9 mcd,indicating that emission intensity higher than that of the LED 10 ofExample 1 was attained. A near field light emission pattern indicatedthat emission intensity was uniform on a virtually entire portion of theemission area other than the pad electrode 107. The emission withuniform intensity was confirmed to be provided from the structure inwhich the bottom portion 107 a provided under the p-type Ohmic electrode107 b serving as an upper portion was formed on the multi-layerstructure including the p-type and high-resistance boron phosphideamorphous layers 105 and 201, whereby device operation current can bedistributed over a wide area of the light-emitting layer 103. Theforward voltage at a forward current of 20 mA was found to be 3.4 V andthe reverse voltage at a reverse current of 10 μA was found to be 8.3 V.

INDUSTRIAL APPLICABILITY

According to the present invention, a boron phosphide-basedsemiconductor crystalline layer is provided via a boron phosphide-basedsemiconductor amorphous layer, and a pad electrode is provided such thatthe bottom portion of the pad electrode is in contact with the surfaceof the boron phosphide-based semiconductor amorphous layer as well aswith the surface of the boron phosphide-based semiconductor crystallinelayer. Thus, excellent bonding between the pad electrode and the boronphosphide-based semiconductor crystalline layer can be attained, anddevice operation current can be distributed over, for example, alight-emission area which is not covered with the pad electrode.Therefore, a boron phosphide-based semiconductor light-emitting devicesuch as a light-emitting diode, which has a wide emission area andattains high emission intensity, can be provided.

1. (canceled)
 2. A boron phosphide-based semiconductor light-emittingdevice, comprising: a crystalline substrate; a first semiconductor layerformed on said crystalline substrate, said first semiconductor layerincluding a light-emitting layer, serving as a base layer and having afirst region and a second region different from said first region; aboron phosphide-based semiconductor amorphous layer formed on said firstregion of said first semiconductor layer, said boron phosphide-basedsemiconductor amorphous layer including a first boron phosphide-basedsemiconductor amorphous layer having a conduction type opposite to thatof said first semiconductor layer; a pad electrode formed on said firstboron phosphide-based semiconductor amorphous layer, for establishingwire bonding; and a conductive boron phosphide-based crystalline layerformed on said second region of said first semiconductor layer, saidconductive boron phosphide-based crystalline layer extending optionallyto a portion of said boron phosphide-based semiconductor amorphouslayer, wherein said pad electrode is in contact with said boronphosphide-based semiconductor crystalline layer at a portion of said padelectrode above the bottom of said pad electrode.
 3. A boronphosphide-based semiconductor light-emitting device as set forth inclaim 2, wherein said boron phosphide-based semiconductor amorphouslayer has a multilayer structure formed from a boron phosphide-basedsemiconductor amorphous layer which is formed so as to attain contactwith said first semiconductor layer and which is of a conduction typeopposite to that of said first semiconductor layer, and ahigh-resistance boron phosphide-based semiconductor amorphous layerformed on said boron phosphide-based semiconductor amorphous layerhaving said opposite conduction type.
 4. A boron phosphide-basedsemiconductor light-emitting device as set forth in claim 2, whereinsaid boron phosphide-based semiconductor amorphous layer is formed of anundoped boron phosphide-based semiconductor.
 5. A boron phosphide-basedsemiconductor light-emitting device as set forth in claim 3, wherein thetwo boron phosphide-based semiconductor amorphous layers constitutingthe multilayer structure of said boron phosphide-based semiconductoramorphous layer are formed of an undoped boron phosphide-basedsemiconductor.
 6. A boron phosphide-based semiconductor light-emittingdevice as set forth in claim 2, wherein said portion of the padelectrode in contact with said conductive boron phosphide-basedsemiconductor crystalline layer is formed of a material able to form anOhmic contact with the conductive boron phosphide-based crystallinelayer.
 7. A boron phosphide-based semiconductor light-emitting device asset forth in claim 6, wherein said portion of the pad electrode formedof a material able to form Ohmic contact with the conductive boronphosphide-based crystalline layer extends onto said conductive boronphosphide-based semiconductor crystalline layer.
 8. A boronphosphide-based semiconductor light-emitting device as set forth inclaim 6, wherein said pad electrode has a bottom portion formed of amaterial able to form non-Ohmic contact with said boron phosphide-basedsemiconductor amorphous layer.
 9. A boron phosphide-based semiconductorlight-emitting device as set forth in claim 2, wherein said padelectrode has a bottom portion provided on said boron phosphide-basedsemiconductor amorphous layer, and an Ohmic electrode portion which isprovided on the bottom portion and which has a center coincident withthat of the plane shape of the bottom portion.
 10. A boronphosphide-based semiconductor light-emitting device as set forth inclaim 9, wherein said Ohmic electrode portion of said pad electrode hasa planar area greater than that of the bottom portion of said padelectrode.
 11. A boron phosphide-based semiconductor light-emittingdevice as set forth in claim 10, wherein said Ohmic electrode portion ofsaid pad electrode extends onto a surface of said conductive boronphosphide-based semiconductor crystalline layer.
 12. A boronphosphide-based semiconductor light-emitting device as set forth inclaim 2, wherein said high-resistance boron phosphide-basedsemiconductor amorphous layer has a resistivity of 10 Ω·cm or more. 13.A boron phosphide-based semiconductor light-emitting device as set forthin claim 12, wherein said high-resistance boron phosphide-basedsemiconductor amorphous layer has a resistivity of 100 Ω·cm or more. 14.A boron phosphide-based semiconductor light-emitting device as set forthin claim 2, wherein said boron phosphide-based semiconductor is selectedfrom the group consisting of B_(α)Al_(β)Ga_(γ)In_(1-α-β-γ)P_(1-δ)As_(δ)(0<α≦1, 0≦β<1, 0≦γ<1, 0<α+β+γ≦1, 0≦δ<1) andB_(α)Al_(β)Ga_(γ)In_(1-α-β-γ)P_(1-δ)N_(δ) (0<α≦1, 0≦β<1, 0≦γ<1,0<α+β+γ≦1, 0≦δ<1).
 15. A boron phosphide-based semiconductorlight-emitting device as set forth in claim 2, wherein said boronphosphide-based semiconductor is selected from the group consisting ofboron monophosphide (BP), boron gallium indium phosphide (compositionalformula: B_(α)Ga_(γ)In_(1-α-γ)P: 0<α≦1, 0≦γ<1), or a mixed-crystalcompound of boron nitride phosphide (compositional formula:BP_(1-δ)N_(δ): 0≦δ<1) or boron arsenide phosphide (compositionalformula: B_(α)P_(1-δ)As_(δ): 0≦δ<1).
 16. A boron phosphide-basedsemiconductor light-emitting device as set forth in claim 6, whereinsaid conductive boron phosphide-based crystalline layer is a p-typeconductivity layer and said portion of said pad electrode in contactwith said conductive boron phosphide-based crystalline layer is selectedfrom the group consisting of Au—Zn and Au—Be.
 17. A boronphosphide-based semiconductor light-emitting device as set forth inclaim 6, wherein said conductive boron phosphide-based crystalline layeris an n-type conductivity layer and said portion of said pad electrodein contact with said conductive boron phosphide-based crystalline layeris selected from the group consisting of Au—Ge, Au—Sn and Au—In.
 18. Aboron phosphide-based semiconductor light-emitting device as set forthin claim 8, wherein said boron phosphide-based amorphous layer is ap-type conductivity layer and said portion of said pad electrode incontact with said conductive boron phosphide-based crystalline layer isselected from the group consisting of Au—Ge, Au—Sn, Au—In, Ti, Mo, V,Ta, Hf and W.
 19. A boron phosphide-based semiconductor light-emittingdevice as set forth in claim 8, wherein said boron phosphide-basedamorphous layer is a n-type conductivity layer and said portion of saidpad electrode in contact with said conductive boron phosphide-basedcrystalline layer is selected from the group consisting of Au—Zn, Au—Be,Au—In, Ti, Mo, V, Ta, Hf and W.
 20. (canceled)
 21. (canceled)